An absolute address signal is recorded on a recording media (a video tape, a hard disk or the like) such as a video tape for broadcasting in a state of a one-to-one correspondence to an image signal for each frame. Accurate edition is carried out based on the absolute signal for the edition of the video tape for broadcasting and non-linear edition utilizing the hard disk.
The absolute address signal is referred to as an SMPTE/EBU time code (which will be hereinafter referred to as a time code), in which SMPTE (Society of Motion Picture and Television Engineers) and EBU (European Broadcast Union) are standardized.
For a method of transmitting an image signal, there has been used a television transmitting method such as a method constituting a frame for one second by 30 frames (which will be hereinafter referred to as a 30 frame/second type) or a method of constituting a one-second frame by 25 frames (which will be hereinafter referred to as a 25 frame/second type). In recent years, furthermore, there has also been used a method for an image of a movie such as a method of constituting a one-second frame by 24 frames (which will be hereinafter referred to a 24 frame/second type).
A time/minute/second/frame is used for the unit of a time code. Each unit of the time code is constituted by a 2-figure number (00/00/00). The digits of time, minute and second are counted in the same manner as in a 24-hour clock. For a frame digit, a frame number per second in the method is counted, and digit-up and down to a second digit are carried out.
In the 30 frame/second type, a time per frame is 33.3 milliseconds. For this reason, one frame has 29.97 Hz (30 Hz: a 1000 msec=xHz: 33.3 milliseconds×30 frames). Therefore, it is impossible to avoid such a situation that a shift is slightly caused between the step of the time code and an actual time. A shift of approximately 108 frames (3.6 seconds) per hour is caused and becomes a problem when an edition work or the like is to be executed for a long time. In the 25 frame/second type and the 24 frame/second type, the shift of the step is not caused because the actual time and the step of the time code are coincident with each other.
In the 30 frame/second type, the following two standards are set to the step of the time code.
A first standard is referred to as a drop mode in which a time code is dropped (removed) corresponding to a shift in order to eliminate the shift of the step. In the drop mode standard, two frames (each minute/00 frame and each minute/01 frame; these frames will be hereinafter referred to as drop frames) are skipped from each positive point (00 second point per minute) excluding 0 minute, 10 minutes, 20 minutes, 30 minutes, 40 minutes and 50 minutes for each hour respectively in order to eliminate the shift of the step between a frame non-coincidence actual time and a time code for a long time (which is equal to or more than a minute). More specifically, a next frame to the 29th frame is not set to be a 00 frame but 02 frame with a jump so that the time code is excessively stepped. Consequently, the shift of the step is eliminated.
A second mode is referred to as a non-drop mode in which the shift of a step present between an actual time and a time on the time code is estimated to utilize the time code. In the non-drop mode, a frame to be skipped is not generated differently from the drop mode.
Thus, the method of transmitting an image signal mixes various methods such as the 24 frame/second type, the 25 frame/second type, the 30 frame/second type (drop mode) and the 30 frame/second type (non-drop mode). For this reason, in the case in which a plurality of image sources are to be prepared for various image production works (edition and the like), it has become difficult to prepare the same standard. Under the circumstances, recently, a converter for converting the standard of an image signal to be recorded again has been desired highly.